spec: Add dnf-bootc subpackage

[evan-goode]

dnf-bootc's only job is to Require python3-gobject-base and ostree-libs, which are needed to check the unlock status on bootc systems. We don't want to add these dependencies on python3-dnf because we don't want them on non-bootc systems, so we use a subpackage.

[jan-kolarik]

Hey, it looks good. The tests are failing due to need for merging bootc branch in libdnf. So it's just a question about how to follow now. You can probably run CI test suite locally with all the bootc changes and then we can merge all remaining PRs, if it's fine. Otherwise, we need to merge libdnf, wait for/trigger nightly builds and see how the tests results will look like.